#include<stdio.h>

int atoi(const char *s)
{
    int result = 0;
    int sign = 1;
    if(*s == '-')
    {
        sign = -1;
    }
    while(*s != '\0')
    {
        if(*s >= '0' && *s <= '9')
            result = result * 10 + *s - '0';
        s++;
    }
    return result * sign;
}

int main()
{
    const char *s = "A12B34";
    // const char *s = "A";
    int a = atoi(s);
    printf("%d\n",a);
    return 0;
}

